rail guns
Rail guns require VERY high voltage/amperage to work. The only ones I have heard of that work are VERY large and have huge generators attached (one APC for the gun and a second for the generator.
Very cool concept but not practical for carry. I have seen advertised velocities at about 14,000 fps. Nearly 3x possible with propellant (gun powder) which has an upper limit of around 5000 fps.